engine and drivetrain Vacuum Leak??

[tomphot]

Hello all - I have recently bought a  '72 2002Tii and I'm having some idle issues - the car runs great  when not at idle, however, once warmed up, it will die at idle which makes me think there may be a vacuum leak.  This is my first BMW and first front engine German car.  Where should I start looking to solve this problem? 

I have great records with this car, the KFish was rebuilt 20,000 miles ago and the engine was new from BMW at the same time which makes me think I need not look in that direction.  

Thanks

[esty]

use a can of carb cleaner or starter fluid and when the car's running, spray a small amount around the hose fittings & connections to the fuel system...if the idle increases when you spray a spot, that's where a vac leak is

https://www.google.com/search?q=finding+vacuum+leak+with+carb+cleaner&ie=utf-8&oe=utf-8

[OriginalOwner]

The tii can be a funny set of nightmares.  My first thought upon reading your post was that the little screw inside the tuna can needs to be adjusted.  Many is the time I made that adjustment to solve/resolve hot-engine-idle headaches.

 

BUT .... beware, it is not always as simple as it sounds.  I started messing with that adjuster back in the days before the internet was invented and I was the only 2002tii owner in town.  And the local dealer mechanic wasn't any help at all, or at least not to me.  So being young and fearless I just started messin' with stuff and discovered that turning that screw just 1/4-turn would solve my hot-engine-die-at-idle problem ..... which sounds like the same problem you describe.

    I also discovered that adjusting that screw would solve the "idle surging" problem.  

 

BUT ..... the performance improvements were not permanently fixed by the adjustments.  For example, I would tune up the engine:  clean the plugs & points, and adjust the points.  Now the engine ran "bad" again, and another adjustment would solve that.  Then as I got a few thousand miles on that tune-up the engine would run "bad" again and I would need another adjustment to solve that.  Back and forth, drove me crazy sometimes.

 

In the present day, I just had my engine rebuilt.  And yep, after 1,500 miles I had to make an adjustment to eliminate "idle surging." 

 

So maybe the tuna can screw adjustment is the "problem" and not any sort of vacuum leak .... and maybe not.  Or maybe both ??  I surely don't know.  But my experience is that what happens on a carburetor car doesn't always translate directly over to the 2002tii.

 

Cheers,

 

Carl

Edited June 12, 2015 by OriginalOwner

[tomphot]

Thanks Carl

I have the detailed instructions that BMWNA put out on adjusting the System - I also don't have the special tools.

Before I start any of that, I'm going on a vacuum leak hunt first.

[Mike87]

It has been my experience that unless the vacuum leak is large the engine will run faster (higher idle). A large vacuum leak will kill the engine almost immediately. So if you suspect a vacuum leak, it will probably be a very large one and should be easy to spot.

 

I am with Carl and your issue lies in an adjustment of the screw in the tuna can. Tiis can be finicky when it comes to adjustments/tuning.

Edited June 12, 2015 by Mike87

[thehackmechanic]

Just to be clear, there are two separate screws on/in the tuna can:

 

--The idle speed adjustment screw is the screw that goes through the outside of the tuna. Once the car is warmed up, the locknut can be released on the screw, and the screw adjusted to put the idle at about 900 RPM.

 

--The the idle mixture screw is the much smaller screw inside the tuna can. Once the car is warmed up, very small adjustments can be made, like 1/16 turn at a time, to make the mixture leaner (screw it in) or richer (back it out). Note that in/lean out/rich is incorrect in the original BMW document. It has been corrected in the version of the document available on the Tii Register. Remember, it's 2015. Lean is in. (Seriously, that's how I remember it.) If the car "hunts" at idle (idle speeds up and slows down), the mixture is probably too lean, and backing the idle mixture screw out until it stops hunting is an absolutely vaild and very effective way to adjust idle mixture. 

 

That having been said, idle speed can be affected by many things -- ignition timing, warm up regulator function, and, yes, vacuum leaks.

 

So, if the idle speed is simply too low, you can put it in the ball park with the idle speed adjustment screw.

 

If, once it's in the ball park, it hunts, you can richen it so it stops hunting by backing out the idle mixture screw slightly. But don't futz with the mixture screw if it's not hunting.

 

(And, yes, there's also a third screw -- the verboten screw on the pump lever arm. Don't touch it without spending at least 80 hours reading every post here on the FAQ, having installed an air/fuel gauge and an oxygen sensor, and having lost a week's worth of sleep because you think your car is too lean at wide open throttle. It's a very exclusive club.)

 

-Rob

[OriginalOwner]

tomphot,

 

those "special KF tools" aren't necessary for tuna can adjustments.  Those tools are for "serious" changes to the KF itself and not for the faint of heart (note Hack's comment re. the very exclusive club).

 

as Hack notes, the tuna can idle speed & idle mixture adjusters are simple and straightforward to adjust.  Especially for the idle mixture inside the tuna can, I would recommend a logbook of each adjustment made.  As Hack notes, even a 1/16th of a turn might have an effect.  One of my frustrations of youth was not keeping track of each adjustment, thus after 3 weeks I couldn't remember if I leaned or richened, or by how much.  So I'd have to mess around trying to find what worked, maddening.

 

OH, I just thought of a location for a vacuum leak, which has plagued me a couple of times.  On the rear of the throttle body there is a small rubber tube which connects to a larger rubber breather hose.  That breather hose goes left-right from the back-end of the valve cover over to the air cleaner box.  The small rubber tube is maybe 3 inches long and hard to see.

     Years ago mine split just a little bit, thus a small vacuum leak.  How I found it I have no clue, but upon replacing that small rubber hose everything was back to normal.

     

For all the experienced tii people:  that small rubber tube:  I cannot find it at   www.RealOEM.com   .... perhaps you know where to look ??

 

Cheers,

 

Carl

Edited June 12, 2015 by OriginalOwner

[thehackmechanic]

Regarding finding vacuum leaks, I just this morning ordered one of these home-built $125 mineral oil-based smoke generators:

 

http://www.ebay.com/itm/EVAP-Smoke-Machine-Diagnostic-Emissions-Evaporative-Leak-Detection-Tester-NEW-/301647516055?hash=item463b97d197&item=301647516055&vxp=mtr

 

I'll let everyone know how well it works.

 

--Rob

[tomphot]

Thanks all - I do have the corrected version of the manual off of the Tii Registry site.

I've got my can of brake cleaner ready for the mornings hunt.

Unfortunately, the only local Atlanta guy I know who knows these systems is way to busy to work on the car, he wants to retire in 2 years and has 5 years of work waiting for him.  He just did some work on my 356 engine for me and I waited a year for that. 

 

The PO had installed a bunch of gauges, only 2 of them are working now, Oil or Water Temp (he told me I could see what I wanted by changing the wiring under the car) and Volts.  The is a Vacuum gauge but it is not showing a reading.  The Vacuum line comes through the firewall and is attached to the small nipple on top of the air cleaner housing - is that the correct spot for that line?  

 

Tom

Edited June 12, 2015 by tomphot

[jgerock]

Since you have a 72tii, please tell us if your engine has the plastic U-shaped intake runners or the later aluminum ones.  The plastic ones tend to leak - hence BMW changing the design to the aluminum bolt on runners.

[tomphot]

The Aluminum ones were installed during the engine install

[jgerock]

The Aluminum ones were installed during the engine install

That is good to know.  

 

Does your car still have the original air cleaner in place?  If so, is there a hose from the valve cover to the air cleaner stub with a small hose to the side of the throttle body?

 

Where are you in the Atlanta Metro area?

[tomphot]

Yes, the original air cleaner is still there and those lines are attached - what's the nipple for on the top of the cleaner?

I'm in the Norcross area.

[Conserv]

... - what's the nipple for on the top of the cleaner?

...

The plastic expansion tank in the trunk -- for evaporative emissions -- has one line running forward to the engine compartment. I believe it goes to the charcoal-filter canister in carbureted cars and the airbox in tii's. So, not having my car here in Atlanta, I'd guess that small nipple on the airbox normally is hooked to the expansion tank.

Regards,

Steve

[tomphot]

That nipple has a tube attached to it that goes to a Vacuum gauge that the PO installed. I was hoping it shouldn't be there and that the tube should be attached someplace else, thus creating a leak that would be easily fixed.